Four fenced pig-free management units and one adjacent unfenced area within the 'Ola'a Forest of Hawaii Volcanoes National Park were systematically searched for rare plants in 1992-94. Additional rare plant sightings were made off transects and on fencelines, while working on other projects in 1995-98. Observations by Resources Management workers were included on maps where possible. Only the western third of the 'Ola'a Forest was searched during this survey, where transects were placed systematically along north/south fence lines at intervals of 250-500 m. Those plants mapped on transects were within a 5-m belt. One listed endangered species, ha'iwale (Cyrtandra giffardii), was found in each surveyed unit, but was concentrated in the Ag and Koa Units below 1,280 m (4,200 K) elevation. 'Ola'a has a larger population of this endangered species than anticipated, as 91 plants were counted along transects. A second endangered species, 'anunu (Sicyos alba), was encountered at four localities within the Koa Unit; this extremely rare vine is known fiom only two other Hawai'i Island sites. Eight former candidate endangered plant species or "species of special concern" were counted along surveyed transects. Only six 'aku (Cyanea tritomantha) were sighted in the Ag and Koa Units. The lobelioid, koli'i (Trematolobelia grandifolia), was more frequently seen, inside and outside the Pu'u Unit and in the lower Ag Unit. One hundred seventeen koli'i plants were counted along transects, and others were sighted off transect. Candidate endangered mints were very rare; only one Phyllostegia floribunda, nine P. vestita, fourteen mohihi (Stenogyne scrophularioides), and six Stenogyne macrantha were observed in the study area. The herb popolo ku mai (Phytolacca sandwicensis) was seen primarily in the Koa Unit, where 10 plants were counted. Only one individual of the vine Schiedea diffusa was found within 'Ola'a at the same Ag Unit site where it was discovered nine years ago; this is the only sighting of the species on Hawai'i Island in more than 80 years. Two endangered species (Adenophorus periens, Clermontia peleana), and three species of concern (Asplenium schizophyllum, Eurya sandwicensis, and Joinvillea ascendens) that were formerly reported from 'Ola'a Forest were not found in the study area in 1992-98. Twenty additional plant species that are rare to uncommon in the Park were sighted within the 'Ola'a Forest study area. Two endemic orchid species (Anoectochilus sandvicensis and Liparis hawaiensis) were each found at only one 'Ola'a site. The rare vine kilioe (Embelia pacifica) occurred at five widely scattered sites in three units. Only 12 individuals of pawale (Rumex giganteus) were observed; half of these were on transects, while others were on fence lines and at sites near transects. Eighty-three pala ferns (Marattia douglasii) were counted along transects; these were concentrated in the Small Tract, Ag Unit, and outside the Pu'u Unit. These large terrestrial ferns are palatable to pigs and are sensitive to disturbance of the forest floor. The lobelioid 'oha kepau (Clermontia hawaiiensis) was noted at only one locality within the Ag Unit, but two other 'oha species (C. montis-loa and C. parviflora) were relatively common in all five units of the study area. Two species of haha or Cyanea were less widely distributed within 'Ola'a Forest. Cyanea degeneriana plants were concentrated in or near the Pu'u Unit and inside the Ag Unit; 60 plants of this species were observed along transects, and a few others were growing on fence lines. Eighty-one Cyanea pilosa subsp. longipedunculata plants were found outside the Pu'u Unit and in the southern half of the Small Tract. Ten of the 20 rare and uncommon plant species of 'Ola'a are shrubs or trees. Papala (Charpentiera obovata) and papala kepau (Pisonia brunoniana), trees more common at mesic sites, were restricted to the Small Tract and the southwestern corner of the Koa Unit. 'Aiea trees (Nothocestrum longifolium) and two species of shrubby kamakahala (Labordia hirtella and L. hedyosmifolia) were widely scattered in all five units of 'Ola'a. Pilo kea (Platydesma spathulata) was very rare within the study area; only 18 pilo kea were noted on transects, and others were encountered off transect. Loulu palms (Pritchardia beccariana) were infrequently encountered, primarily in the Small Tract, Koa, and Ag Units. 'Ohe mauka (Tetraplasandra oahuensis) trees, with one exception, were restricted to the Pu'u Unit, where 19 individuals were counted along transects and fence lines. Two members of the nettle family were also mapped along transects. Olona (Touchardia latifolia) was most often seen within the Ag Unit, but was also scattered throughout the Koa Unit and Small Tract and was sighted once outside the Pu'u Unit. Opuhe (Urera glabra) was much rarer and was concentrated in the eastern half of the Small Tract and the adjacent area in the Koa Unit. Only 11 widely scattered individuals of maua (Xylosma hawaiiense), a tree also known from mesic forests, were sighted within the study area.

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